China has shut down more than 70 percent of its first 5,000 collieries to be announced unsafe, a senior official in charge of the country's coal mine safety said on Tuesday.

"China will step up efforts to close down those small coal mines without a safe production license," said Wang Shuhe, deputy director of the State Administration of Coal Mine Safety Supervision.

According to a statement issued in 2005 by the State Council, China's cabinet, more than 5,000 small dangerous collieries had to be closed before the end of 2005.

Due to various factors, however, some small problematic coal mines are still operating across the country, said Wang, noting that those left must be shut down by the end of March.

To close such small collieries is aimed at improving the safety conditions and changing the structure of China's coal-mining industry, he said.

Wang was on an inspection tour for coal mine safety in north China's Inner Mongolia Autonomous Region, where an explosion at a privately-run colliery in the region's Wuhai City occurred at 3:25 a.m. on Monday, killing at least 18 of its 34 miners working underground.